Radio communications systems are increasingly being used for wireless mobile communications. An example of a radio communications system is a cellular phone network. Cellular radio communications systems are wide area communications networks which utilize a frequency (channel) reuse pattern. The design and operation of an analog cellular phone system is described in an article entitled Advanced Mobile Phone Service by Blecher, IEEE Transactions on Vehicular Technology, Vol. VT29, No. 2, May, 1980, pp. 238-244. The analog mobile cellular system is also referred to as the "AMPS" system.
Recently, digital cellular phone systems have also been proposed and implemented using a Time-Division Multiple Access (TDMA) architecture. Standards have also been set by the Electronics Industries Association (EIA) and the Telecommunications Industries Association (TIA) for an American Digital Cellular (ADC) architecture which is a dual mode analog and digital system following EIA/TIA document IS-54B. Telephones which implement the IS-54B dual mode architecture are presently being marketed by the assignee of the present invention. Different standards have been promulgated for digital cellular phone systems in Europe. The European digital cellular system, also referred to as GSM, also uses a TDMA architecture.
Proposals have recently been made to expand the cellular phone network into a radio personal communications system. The radio personal communications system provides mobile radio voice, digital, video and/or multimedia communications using radio personal communications terminals. Thus, any form of information may be sent and received. Radio personal communications terminals include a radio telephone, such as a cellular telephone, and may include other components for voice, digital, video and/or multimedia communications.
A radio personal communications system includes at least one telephone base station also referred to herein as a base station. A base station is a low power transceiver which communicates with a radio personal communications terminal such as a cellular telephone over a limited distance, such as tens of meters, and is also electrically connected to the conventional public wire network. The base station allows the owner of a radio personal communications terminal to directly access the wire network without passing through the cellular phone network, whose access rates are typically more costly. When located outside the range of the base station, the personal communications terminal automatically communicates with the cellular phone network at the prevailing access rates.
A major problem in implementing a radio personal communications system using a common frequency allocation for both the base station and the cellular phone network is the frequency overlap between the cellular phone network and the base station. As understood by those having skill in the art, only a limited number of frequencies are available for radio communications. In the United States, cellular phone networks have been allocated 832 30 kHz wide channels. Within this spectrum, each regional provider can substantially allocate and use these frequencies as it sees fit. Additional ranges of frequencies are also being allocated in the United States for use as wide area cellular communications networks.
Cordless phones, such as those used by individuals in their homes, utilize a separate range of frequencies, in the United States from 46 MHz to 49 MHz. Therefore, they are able to operate within a cellular network without interference. However, such phones are unable to operate as cellular phones connected to the cellular network when out of range of their individual base stations. Dual mode phones which operate both as a cellular phone within the cellular frequency range (824-894 MHz) and as a conventional cordless phone (46-49 MHz) are described in U.S. Pat. No. 4,989,230 to Gillig et al.
Frequency overlap between the network and the base stations can be prevented if the network and base stations are allocated different bands of frequencies as with the dual mode cellular and cordless phone discussed above. However, such a hybrid system is not an efficient allocation of the frequency spectrum. Moreover, a hybrid personal communications terminal may be more expensive and complicated because additional circuitry may be required.